Field of the Invention
The present invention relates generally to the field of surgical repair of retinal disorders, and more specifically to the efficient operation of pneumatic vitrectomy devices during ophthalmic surgical procedures.
Description of the Related Art
Vitrectomy surgery has been successfully employed in the treatment of particular ocular problems, such as retinal detachments resulting from tears or holes in the retina. Vitrectomy surgery typically involves removal of vitreous gel and may utilize three small incisions in the pars plana of the patient's eye. These incisions allow the surgeon to pass three separate instruments into the patient's eye to affect the ocular procedure. The surgical instruments typically include a vitreous cutting device, an illumination source, and an infusion port.
Current vitreous cutting devices may employ a “guillotine” type action wherein a sharp-ended inner rigid cutting tube moves axially inside an outer sheathing tube. When the sharp-ended inner tube moves past the forward edge of a side port opening in the outer sheathing tube, the eye material (e.g. vitreous gel or fibers) is cleaved into sections small enough to be removed through the hollow center of the inner cutting tube.
Vitreous cutters are available in either electric or pneumatic form. Today's electric cutters may operate within a range of speeds typically between 750-2500 cuts-per-minute (CPM) where pneumatic cutters may operate over a range of speeds between 100-2500 CPM. The surgeon may make adjustments to control the pneumatic vitrectomy surgical instrument cutting speed, i.e. controlling the cutting device using a surgical handpiece, in order to perform different activities during the corrective procedure. Corrective procedures may include correction of macular degeneration, retinal detachment, macular pucker, and addressing eye injuries.
The cutting device within a pneumatic handpiece requires precise control of applied pressure to overcome the internal spring return mechanism to assure the quality of each cutting stroke. Such systems have typically employed a fluid (typically air) reservoir or accumulator to collect fluid and from which fluid is drawn to effectuate the cut valve using pneumatic pressure. The frequency of opening and closing the pneumatic valve, i.e. the time interval between each opening cycle of the valve, is varied to achieve the desired cutting speed. In order to power the cut valve and cutter at a consistent pressure for an extended period of time, a relatively large fluid reservoir or accumulator is needed. A large fluid reservoir is undesirable in today's operating environment where smaller components are favored. Further, in this type of environment, inconsistent pressure can be provided to the cut valve in even the best of circumstances, and in the case of minor leaks, inconsistent pressure is practically a given. Even minor pressure inconsistencies can be highly undesirable.
Additionally, current systems employ calibration settings to account for changes in the operating room environment. Calibration settings can accommodate for relatively fixed environmental factors, such as altitude, but rapidly changing environmental factors such as temperature or electro-mechanical pump variations in virtually all situations cannot be adequately addressed using calibration techniques.
Based on the foregoing, it would be advantageous to provide a system that enables pneumatic cutting functionality at relatively consistent cutting pressures that reduce or eliminate the need for a relatively large fluid reservoir or accumulator. Such a system would have an ability to provide consistent cutting pressures under different conditions typically encountered in a vitrectomy surgical room environment.